A Hirshfeld-I interpretation of the local moment composition of the quadrupole moments of the halogenated acetylenes FCCF, ClCCCl, BrCCBr, and ICCI

作者：Harrison James F^*

来源：Computational and Theoretical Chemistry, 2012, 999: 83-88.

DOI：10.1016/j.comptc.2012.08.017

• Hirshfeld
• Quadrupole moments
• Halogenated acetylenes

We have interpreted the molecular quadrupole moments of the di-halogenated acetylenes, XCCX, where X = F, Cl, Br, and I as well as the parent HCCH in terms of the in situ atomic moments (charge, dipole and quadrupole) calculated with the Hirshfeld-I partitioning of the electron density. The conclusion from this analysis is that the SCF and CCSD molecular densities are similar and predict comparable atomic densities and in situ moments. We find that the sigma charge on carbon decreases monotonically with the electronegativity difference between carbon and the substituent X, being positive for X = F, Cl and Br and going negative for X = I and H. The pi charge on carbon is negative for all of the halogens and positive for H, reflecting the opportunity for back donation in the halogens and the lack thereof in H. The contribution of the three localized moments to the molecular quadrupole moments of ClCCCl, HCCH, BrCCBr and ICCI are all positive resulting in positive quadrupole moments while the negative quadrupole moment of FCCF is due to cancelation between the large negative contribution of the charge and the positive induced dipole, quadrupole terms. The HI charges are significantly different from the point charges obtained from fitting the molecular quadrupole moments. Additionally we show that the computed in situ atomic quadrupoles may be used to assign an electronic configuration to the in situ atoms.

• 出版日期2012-11-1